There was a time when the air was thick with pollutants you could see, smell and even taste. When air pollution was collected in buckets and measured in inches.

For Kentucky, those days are long past. Air quality today is dramatically – and measurably – cleaner than it was 50, 20 or even 10 years ago.

How do we know?

At the heart of the Division for Air Quality’s mission to protect clean air for Kentucky is an electronic army of air monitors spread across the Commonwealth. These sophisticated machines (and their human handlers) collect and analyze thousands of air samples each day.

Tasting and Vacuuming the Air

At its simplest, an air monitor measures air pollution in the ambient or outdoor air. The Clean Air Act requires monitoring for six criteria pollutants – ozone, particulate matter, nitrogen dioxide, sulfur dioxide, carbon monoxide, and lead – as well as volatile organic compounds (VOCs), which contribute to ozone pollution.

Monitors use different methods for different pollutants. Some monitors use chemistry to “taste” the air, while others use a vacuum to pull the air through a filter, which is later weighed. Still others collect air in canisters to be analyzed in a lab.

Some monitors collect data continuously, while others collect samples on an hourly or daily basis. With a network of 119 monitors across the Commonwealth, that adds up to a lot of data. A single month might see as many as 195,000 unique measurements across the entire network.

Weather is an important piece of the puzzle, too. Pollutants can be carried by wind and influenced by temperature. Weather instruments at several monitoring sites track wind speed and direction, ambient air temperature and humidity.

Minding the Monitors

For more than 18 years, Environmental Inspector Joe Boggs has tended to the air monitors in eastern Kentucky’s Ashland region. Boggs’s official job title doesn’t begin to tell the story of all that he does. Data checker, sample collector, instrument trouble-shooter and groundskeeper- Boggs does it all in his day to day work as an air monitoring specialist. Boggs’s job is hands-on, and that’s what he loves about it.

“It’s never the same thing twice,” Boggs said. “I love working with the instruments, solving problems and keeping everything running smoothly.”

Being outdoors is another plus. One of Boggs’s monitoring sites happens to be nestled in a scenic area near Grayson Lake in Carter County. The remoteness of this site means air quality measurements here can be used as a baseline for normal, background conditions of pollutant levels. “It’s not unusual for a bald eagle, fox or bobcat to pass by while I’m working on the monitors here,” he said.

One of Boggs’s jobs is to collect and restock filters for the PM2.5 sampler. PM2.5 is shorthand for fine particulate matter that measures less than 2.5 microns in diameter. Because it is so tiny, PM2.5 can be inhaled deep into lungs and lead to serious health problems.

While many air monitors send data electronically to computers at regional air quality offices, the PM2.5 sampler requires regular visits by a field inspector like Joe to change filters, clean and calibrate the instrument.

This sensitive instrument works by pulling a measured volume of air through a pre-weighed filter for a period of 24 hours. Before reaching the filter, the air passes through a chamber where larger particles fall out of the air stream. Particles less than 2.5 microns pass onto the filter, where they are collected.

Once the sample has been taken, the instrument stores the filter in a canister until Boggs retrieves it. “As soon as I collect the filters, I bag and label each one with the date and time of sampling. Then we ship them to a laboratory for weighing again,” Boggs said. Keeping the filters cool en route is essential, since some particulate matter is composed of liquid droplets that may evaporate in warmer temperatures.

By subtracting the starting weight of the filter from its ending weight after sampling, it is possible to determine exactly how much PM2.5 was collected.

A Network of Monitors

Most of Kentucky’s ambient air monitoring sites are nowhere near as scenic and remote as Grayson Lake. Urban sites are far more typical.

Kentucky’s air monitoring network includes 34 monitoring stations in 26 counties; this includes monitors operated by the Louisville Metro Air Pollution Control District and by the National Park Service at Mammoth Cave.

Federal regulations outline specific requirements for siting air monitoring stations (40 CFR Part 58). In general, air monitors are placed in densely populated areas or near major sources of pollution, whether it’s a busy highway or a stationary source with a smokestack.

Each year, Division staff review the site locations of each air monitoring station to ensure that adequate coverage is being provided and regulatory requirements are met. Environmental scientist Jennifer Miller coordinates these efforts with the Ambient Air Monitoring Network Plan.

“We’re very strategic in where we place these air monitoring stations,” Miller said. “Knowing the locations of major pollution sources and population centers helps us pinpoint the best locations for monitoring. Adding wind and weather data to the mix, we can use air dispersion modeling as a tool to characterize air quality in counties without air monitors.”

Ultimately, it all comes down to the data, and that data tells a remarkable story of air quality improvement in the Commonwealth over the last several decades. Monitored pollution levels in Kentucky have dropped significantly since the Clean Air Act was adopted in 1970, even as population and energy consumption have increased.

For example, sulfur dioxide and nitrogen oxide emissions from Kentucky coal-fired power plants have decreased more than 75 percent in the past 25 years, thanks to better pollution controls and recent power plant retirements.

At the same time, air pollutant standards are much tighter today than they were decades ago. “If today’s ozone standards had been in effect in 1970, virtually every monitor in Kentucky would have registered violations with those standards,” said Miller. “In contrast, all but one of our ozone monitors is currently showing compliance.” A single monitor in Boone County is not meeting the recently-strengthened ozone standard.

“Without our air monitoring network, we would still be guessing about air quality,” said Miller.